The present invention relates to a shortcut routing method over an Internet network as described in the preamble of claim 1 and a related device as defined in the preamble of claim 2.
Such a shortcut method, related device and related system are already known in the art, e.g. from the internet draft document xe2x80x9cIPSOFACTO: IP Switching over Fast ATM cell transportxe2x80x9d from the authors A. Acharya, R. Dighe and F. Ansari, published in July 1997 by Internet Engineering Task Force (IETF). Therein, a method for mapping of IP multicast-flows to ATM connections is described. This method refers to constructing an Internet Protocol multicast distribution tree for each source and the shortcut routing along each of the branches of the constructed tree. This distribution tree, called a point-to-multipoint VC in the referred draft, is a tree from the multicast-source at the root of the tree to all multicast receivers, as leaves of the tree. The distribution tree provides the shortest path from the source to each receiver of the group. It should be noticed that the Internet Protocol hereafter is called IP. The just mentioned tree is constructed and maintained using a xe2x80x9cbroadcast and prunexe2x80x9d technique, where broadcast is called xe2x80x9cadding a point-to-multipoint VC entry in the hardware VC routing tablexe2x80x9d, when a source starts to send to a multicast group. This means that the multicast-source sends a broadcast message to each receiver of the group. Each receiver not interested, sends a prune-message in the direction of the sender indicating to be excluded from the multicast-group. In case of an IP-multicast shortcut all tree topology information is copied from OSI layer 3 to OSI layer 2, called xe2x80x9cmapping the state to a point-to-multipoint VC within the switching fabricxe2x80x9d in the draft. Thus for a broadcast message towards each receiver a shortcut over an ATM shortcut VC is set-up. For each receiver not interested sending back a prune-message the shortcut over the ATM shortcut VC is released, called xe2x80x9cdeleting a VC from the VC routing tablesxe2x80x9d.
In the current situation, that is the situation as described in the prior art the shortcut path is set-up at a certain moment in time. The receiving host which is not interested indicates this by sending a prune-message. In the end it can be concluded that setting-up the shortcut path towards this receiving host wasn""t necessary and superfluously using network resources.
An object of the present invention is to provide a shortcut routing method of the above known type but which is performed more efficiently and wherein less network resources are used superfluously.
According to the present invention, this object is achieved by the method as described in claim 1 and the device as described in claim 2.
Indeed by delaying the set-up of a shortcut path, while the delay-time is for instance at least the period of time a prune-message, sent by the receiving host, needs to reach the initiating upstream router, it is avoided that shortcut paths are set-up useless. Hence, if the set-up of the shortcut path is delayed till a potential prune-message can be received, no shortcut path is set-up superfluously.
A further characteristic feature of the present invention mentioned in claim 3, is also related to the determination and adaptation of the delay time-interval.
The shortcut router ROU may be able to determine an expiration-time of a prune-message, that is the period of time a prune-message is received by the sending host SH after expiration of the delay-time interval. If the shortcut router ROU receives a number of prune-messages after or before the expiration of the current delay time interval, the delay-time interval can be adopted in order to optimise the establishment of shortcut connections. Based on this expiration-time the shortcut router ROU calculates the measure of extension of the delay time-interval. Another possibility might be the situation that prune messages are received before the expiration of the delay-time. The delay time-interval can be decreased then.
Also an additional feature of the present invention is described in claim 4.
A shortcut router device may be involved in the set-up of more than one shortcut path, one between the sending host and each of the receiving hosts To take, the delay times of each of the parallel shortcut path""s branches of the multicast tree wherein the mentioned shortcut router device is involved, into account each shortcut router device includes a delaying means for each path between the sending host and a receiving host.